1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device for displaying, by projecting an image held by an image holding means, on a screen.
2. Description of the Prior Art
FIG. 1 is a diagram showing an optical composition of a first prior art liquid crystal display using a liquid crystal light valve 5 possessing a photoconductor layer. When displaying an image on the liquid crystal display device, the image displayed on a cathode ray tube (CRT) 51 enters into the liquid crystal light valve 5 by way of a lens 52.
FIG. 7 is a sectional view showing the composition of a liquid crystal light valve 5. In the composition of the liquid crystal light valve 5, transparent electrodes 22a, 22b, composed of a transparent conductive film of indium tin oxide (ITO), are formed on glass substrates 21a, 21b, and a hydrogenated amorphous silicon (a-Si:H) is formed on the transparent electrode 22b as photoconductor layer 25. The hydrogenated amorphous silicon is made of silane gas and hydrogen gas, and is fabricated by employing the plasma CVD method. On its surface, a multilayer film of silicon/silicon oxide is formed by a sputtering method, as a dielectric mirror 24.
After forming polyimide films, by spin coating, as orientation films 23a, 23b, the molecular orientation is processed by rubbing, and the glass substrates 21a, 21b are glued together by way of a spacer 27. By injecting and sealing a mixed nematic liquid crystal containing chiral material as the liquid crystal layer 26, the liquid crystal light valve 5 is thus composed. As the operation mode of the liquid crystal light valve 5, the hybrid field effect is employed.
Between the transparent electrodes 22a, 22b of the liquid crystal light valve 5 composed in such a structure, a voltage is applied from an AC power source 28. When the image from the CRT 51 enters from the glass substrate 21b side as mentioned above, the impedance of the photoconductor layer 25 varies depending on the quantity of incident light. As a result, the voltage to be applied to the liquid crystal layer 26 changes, and the orientation state of the liquid crystal is modified. Thus, an image corresponding to the image from the CRT 51 forms on the liquid crystal layer 26.
When light from a light source 54 enters the liquid crystal light valve 5 in which the image is thus formed, by way of a lens 55 and a polarization beam splitter 56, this incident light is reflected by the dielectric mirror 24. Further, the portion of this light reflected after passing through the orientation changed part of the liquid crystal layer 26 changes in polarization direction by the electro-optical effect. Thus it passes through the polarization beam splitter 56. This reflected light is magnified by a lens 57, so that the image formed on the liquid crystal light valve 5 is thereafter projected on the screen 58.
FIG. 2 is a diagram showing an optical structure of a liquid crystal display device of a second prior art device. This second prior art device is similar to the first prior art device, and the corresponding parts are identified with the same reference numbers. In the second prior art device, an image is formed on the liquid crystal light valve 5 by means of a laser beam 59.
In the first prior art device, since the resolution of the image displayed by the liquid crystal display device is determined by the resolution of the CRT 51, it is difficult to enhance the resolution. Further, since it is necessary to incorporate the CRT 51 into the liquid crystal display device, it is difficult to reduce the liquid crystal display device in size.
In the second prior art device although the resolution may be improved by reducing the irradiation area of the laser beam, additional space for accommodating the laser beam control mechanism is necessary, and hence it is difficult to reduce the liquid crystal display device in size.